Exam 19: The Inheritance of Complex Traits

Two pure lines of Nicotianum (tobacco)have significantly different corolla lengths.In line 1,the average length is 30 mm,ranging from 25 mm to 35 mm with a variance of 10.In line 2,the average corolla length is 60 mm,ranging from 45 mm to 65 mm with a variance of 12.The F₁ has a corolla length of 45 mm,ranging from 40 to 50,and the variance is 9.Upon selfing,an F₂ is produced that has an average flower length of 45 mm,but ranges from 10 mm to 80 mm with a variance of 55. a)Provide a general explanation of these results. b)Calculate the broad-sense heritability (H²)for corolla length in this study.

An individual plant is heterozygous for loci that affect height and have a strictly additive mode of action.If this plant is selfed,: a)how many height classes will there be among the progeny? (Assume no environmental effects.) b)what will be the frequency of the tallest class of progeny? (Assume no environmental effects.)

In an experiment carried out in a chicken population,measurements of fat content reveal that the genetic variance for this trait is 120 g²,the environmental variance is 80 g² and the variance due to dominance is 38 g².The narrow-sense heritability (h²)of fat content in these chickens is:

The variance in tail length in a large population of genetically diverse mice is found to be 21.30.The broad-sense heritability for this trait in an identical population was found to be 0.8.Based on this information,what is the predicted genetic variance (V_g)for these mice?

In the course of estimating the degree of linkage of a marker and a quantitative trait of interest,researchers announced that they obtained a LOD score of 4.5.This finding indicates that:

Consider a diploid fish in which tail length is solely controlled by the additive action of two unlinked loci,F (f)and G (g),without any effect of the environment.A female of genotype F/F;G/G,with a 3 cm long tail,is crossed to a male of genotype f/f;g/g,with a 2 cm long tail.All the F₁ fish have 2.5 cm long tails. a)If the F₁ fish are crossed to each other,how many different tail length phenotypes will be present in F₂?

Which of the following statements is/are a central assumption of the multifactorial inheritance hypothesis?

Loppins (fictitious diploid invertebrates)have variable numbers of dots on their abdomen.This variability is entirely due to genetics,with no influence of the environment,so the broad-sense heritability for this trait is 1.The mean number of dots per individual in a large population is 37.A breeder crosses the two animals with the highest number of dots,45.In the progeny,the mean number of dots is 43.4.These results suggest that the phenotype of interest is controlled:

In a natural population of outbreeding annual plants,the variance of the total number of seeds per plant is 16.From the natural population,20 plants are taken into the laboratory and each selfed for 10 generations.The average variance in the tenth generation in each of the 20 sets is about equal,and averages 5.8 across all the sets.Estimate the broad-sense heritability (H²)of seed number in this population.

a)What is the role of marker genes for the identification of quantitative trait loci? b)How do they differ from candidate genes?

Two different pure-breeding lines of tobacco were crossed and their F₁ showed a variance in flower length of 8.76.The total variance in flower length in the F₂ was 40.96.The F₁ and the F₂ plants were bred,grown,and kept in identical environments. a)What is the broad-sense heritability of flower length in tobacco in this experiment?

It is difficult to measure any type of heritability without the ability to perform specific crosses.However,vast population studies enable estimation of heritability for some characters in human beings.Some estimated broad-sense heritabilities include: Character stature 0.85 body weight 0.62 systolic blood pressure 0.57 diastolic blood pressure 0.44 twinning 0.50 Which of these characteristics is most likely to "run in families"?

Three populations of true-breeding C.elegans larvae are each split into four subpopulations of equal sizes,and each subpopulation is grown in a different environment.The mean adult body lengths in each environment are as follows: Based on these data,what environment has the highest environmental deviation?

Narrow-sense heritability (h²)is a quantification of the proportion of total variance due to:

The phenotypic deviation that is transmitted from parents to their offspring is known as:

In a population of beetles,the total variance of body weight is 130.It is estimated that the environmental variance is 35,and dominance genetic variance is 45.Calculate the narrow-sense heritability (h²)of body weight in these beetles.